1. Field
The present disclosure relates to a fuel cell system and a driving method thereof. More particularly, the present disclosure relates to a fuel cell system configured to be driven under sub-zero temperature conditions, and a driving method thereof.
2. Description of the Related Technology
A fuel cell is a device that electrochemically produces power using fuel (hydrogen or reformed gas) and an oxidizing agent (oxygen or air) continuously supplied from the exterior of the device. Namely, the fuel cell directly converts the fuel and the oxidizing agent into electrical energy through an electrochemical reaction. The oxidant of the fuel cell includes oxygen or air containing a large amount of pure oxygen. The fuel includes a large amount of hydrogen generated by reforming pure hydrogen or a hydrocarbon-based fuel (LNG, LPG, CH3OH).
One type of fuel cell is a polymer electrode membrane fuel cell (PEMFC). The polymer electrolyte membrane fuel cell has high output density and high energy transformation efficiency, and is operable at a temperature of 80° C. or less. In addition, the polymer electrolyte membrane fuel cell can be miniaturized and sealed. Thus, the PEMFC has been widely used as a power source for a variety of applications such as for a pollution-free vehicle, home power equipment, mobile communication equipment, military equipment, medical equipment, and the like.
The PEMFC includes a membrane electrode assembly (MEA) in which an electrochemical reaction is performed. When the fuel cell stack is driven at a sub-zero temperature, the MEA does not perform a fluent reaction, which makes generation of sufficient energy and heat difficult. When the fuel cell stack is continuously exposed to sub-zero temperatures and fails to generate sufficient heat, it will stop generating electricity. The electrochemical reaction, which under normal conditions also generates water as well as heat and electricity, will stop producing water. Water generated at the sub-zero temperature will freeze into ice, which further interferes with the electrochemical reaction. Also, the formation of ice causes the volume of water to expand, which may damage the major components of the fuel cell, particularly the MEA. For the PEMFC, water plays an important role in conducting protons. If the water in the PEMFC freezes, the protons cannot be conducted and no electricity can be generated.
The above information disclosed in this Background section is only for enhancement of understanding and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.